And wrote a kind of API system where you can do with an API Key something great.

All functions are also available separately!

Now I wanted to offer all right fine. Talk to user management, group management, rights management, management modules, and of course, "Management Accounting" if someone wants to use more than just basics ^^.

Is there a quite simple CMS that ensures high levels of safety, well clear with SSL and all my wishes come true? Or do I have to also build by my own xD?

Some edge Info:

The whole is to be expanded quite large. I dont wanna say that could be but i wanna be prepared for it. Say..., more than 10000 people wanna use this in same time, then the cms have to manage this without problems (low loading times). Only few DB queries! Easily expandable. Template etc easily to insert :-)

Best directly multilingual and possible different template to load like mobile templates.

Oh I do not necessarily always want to access the API, because the already could be used extreme, it would be just fine - so like components have areas for them own applications / functions (Internal) is best even with "Cache."

Well ... even more wishful thinking but it would be heck first

Can anyone suggest a fine as a CMS?

edit:
I have the last week completely filled with stress tests (hope my hoster does not cry xD) and so shot around 500,000 requests per day on the application, which it has survived well - would be really top if the CMS can handle this to without problems or leaks -> particularly what charging time is concerned. For me, everything is really slow over 3sec! Even when the cache process should not exceed 3 seconds.